<template>
    <ul class="list">
       <li @touchstart.prevent="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd"
        @click="handleLetterClick" class="item" v-for="item in letters" :key="item" :ref="item">
        {{item}}</li>
    </ul>
</template>
<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  update () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) { // 鼠标在字母表上移动，延迟10毫秒更新城市数据
      if (this.timer) {
        clearTimeout(this.timer)
      }
      this.timer = setTimeout(() => {
        const touchY = e.touches[0].clientY - 79
        const index = Math.floor((touchY - this.startY) / 20)
        if (index >= 0 && index < this.letters.length) {
          this.$emit('change', this.letters[index])
        }
      }, 8)
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>
<style lang="stylus" scoped>
 @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
